This invention is directed to jet engines and, more particularly, to thrust reversers for jet engines. While the invention finds its primary use in reversing the fan air flow of a fan jet engine, and is mainly described in such an environment, it will be appreciated that it can be used in other environments and for other purposes. For example, it can be used in a STOL (short take-off and landing) aircraft environment to assist in primary air flow control, as hereinafter described.
Various types of apparatus have been proposed for reversing the thrust of jet engines. One of the most common devices for reversing the fan air flow of a fan jet engine includes cascades formed in the engine nacelle and a means for exposing the cascades when reverse thrust is desired, in combination with a mechanism for blocking fan air flow in the fan air duct rearwardly of the cascades. In general, such prior art devices expose the cascades by moving or retracting a cover, usually formed of a heavy ring surrounding the nacelle, rearwardly. As the cover is retracted rearwardly, blocker doors are moved to a position whereat they block the normal fan air duct outlet. One of the major disadvantages of this structure is the weight created by the relatively heavy cover utilized to control the exposure of the open cascades and the heavy mechanism needed to operate the cover. A further disadvantage relates to the length of the path of travel traversed by the cover. Specifically, because the longitudinal distance of this path is substantial, it places undesirable restrictions on engine design.
Various proposals have been made to overcome the foregoing disadvantages. In this regard, it has been proposed to expose or open a plurality of cascade elements by rotating them between open and closed positions rather than withdrawing a cover ring. When such cascade elements are rotated to their open position, they define flow paths that direct fan air from the fan air duct toward the front of the engine nacelle, i.e., they reverse fan air flow. An example of such a system is described in U.S. patent application 521,264, entitled "Jet Engine Thrust Reverser" by Claude R. Stachowiak, filed Nov. 6, 1974 and assigned to the assignee of the present application. While this and other similar prior art systems propose an alternative to the mechanism of more classical thrust reversers, they also have certain disadvantages. This invention is directed to overcoming these disadvantages.
Therefore, it is an object of this invention to provide a new and improved air flow control mechanism.
It is another object of this invention to provide a new and improved exhaust air flow control mechanism for a jet engine.
It is also an object of this invention to provide a new and improved rotatable cascade element thrust reverser for use in reversing the fan air flow of a jet engine.
One of the major disadvantages of previously proposed rotatable cascade mechanisms relates to the difficulty of sealing the cascade elements, particularly when they are in their closed position. More specifically, if the cascade elements are not adequately sealed, fan air will escape from the fan air duct in the region of the cascade elements when such escape is undesired; specifically, when the cascade elements are in their closed position.
Therefore, it is a further object of this invention to improve the sealing of rotatable cascade element thrust reversers.
Another problem with prior art rotatable cascade element thrust reversers, also related to sealing, is the prior art's failure to provide a sealing mechanism that provides for venting fan air in the region of the cascade elements just prior to their being rotated open. More specifically, the internal pressure on closed, rotatable cascade elements, created by fan air, tends to lock them closed. Obviously, either the forces creating this pressure must be reduced or the cascade elements must have structural strength (and be driven by a power source) adequate to withstand such forces.
Therefore, it is an object of this invention to provide a sealing mechanism suitable for sealing rotatable cascade elements that provides for venting in the region surrounding the cascade elements and, thereby, reduces the fan air force applied to the cascade elements.
Another prior art disadvantage of some rotatable cascade thrust reversers relates to their basic cross-sectional configuration. In this regard, it will be appreciated by those skilled in the art that certain cascade opening size criteria must be met in order to avoid undesirable pressure buildups during thrust reversal. Some prior art proposals for rotatable cascade thrust reversers have not been able to meet these criteria when reduced to practical embodiments.
Therefore, it is another object of this invention to provide a rotatable cascade element thrust reverser wherein the cascade elements have an adequately large exhaust opening size.
A still further disadvantage of many prior art systems of the type contemplated by the invention is their requirement that they be adjusted while affixed to their associated jet engine, rather than being adjusted at some remote (bench) location.
Therefore, it is still a further object of this invention to provide a rotatable cascade element thrust reverser formed in a manner such that it can be removed and adjusted at a remote location.
Another problem with prior art thrust reversers of various types relates to the nature and complexity of the blocker doors used to block the fan air duct during thrust reversal.
Therefore, it is still another object of this invention to provide new and improved blocker doors for a thrust reverser suitable for use in combination with a jet aircraft engine.
It is a still further object of this invention to provide new and improved blocker doors suitable for use in the fan air duct of a turbofan engine that are uncomplicated, yet are readily movable between open and closed position.